1. Field of the Invention
The present invention generally relates to mobile equipments, base station apparatuses and communication control methods, and more particularly to a mobile equipment, a base station apparatus and a communication control method that are applicable to a digital radio communication system such as the Long Term Evolution (LTE) system.
2. Description of the Related Art
Recently, the third generation portable telephone (International Mobile Telecommunications 2000 (IMT-2000)) system employing the Wideband Code Division Multiple Access (W-CDMA) system is becoming the mainstream of the mobile radio communication. In view of this trend, the 3rd Generation Partnership Project (3GPP), that is the standardization body for the third generation mobile communication system, is adjusting the specifications related to the LTE system so as to realize an even faster communication and to provide a higher quality service. The LTE is the next generation communication system that is also referred to as a Super 3G, S3G or 3.9G.
FIG. 1 generally shows an existing LTE system. The LTE system shown in FIG. 1 includes access gateways (aGWs) 20 (201, 202) provided in a Core Network (CN) 10, base station apparatuses 30 (300, 301, 302, 303), and a mobile equipment 40. The access gateways 20 and the base station apparatuses 30 form an LTE Radio Access Network (LTE-RAN) 35.
FIG. 2 generally shows an existing IMT-2000 that is the mainstream of the mobile radio communication system. The IMT-2000 system shown in FIG. 2 includes a switching system 60 provided in a Core Network (CN) 10, Radio Network Controllers (RNCs) 70 (701, 702), base station apparatuses 80 (800, 801, 802, 803), and a mobile equipment 90. For example, a Japanese Laid-Open Patent Application No. 2004-135292 proposes such an IMT-2000 system.
As may be seen by comparing FIGS. 1 and 2, the IMT-2000 system is provided with the radio network controllers 70 that do not exist in the LTE system.
In future mobile radio communication systems typified by the LTE system, it is desirable to simplify the network structure as much as possible. By simplifying the network structure, it would be possible to reduce the number of nodes arranged within the network, improve the communication quality, and improve the maintenance requirements.
For this reason, in the LTE system, the radio network controllers are eliminated, and instead, a portion of the functions provided in the radio network controllers is implemented in the base station apparatuses.
The radio network controller 70 of the IMT-2000 system has an important function related to the mobile control, which is one of the important functions of the mobile communication system. More particularly, the radio network controller 70 manages information of the base station apparatuses 80 and the mobile equipment 90 that are under the control of the radio network controller 70, radio resource allocation states and the like. The radio network controller 70 carries out the mobile control with respect to the base station apparatuses 80 and the mobile equipment 90 based on such information managed by the radio network controller 70. Accordingly, the radio network controller 70 needs to store all of the information related to the base stations 80 that are under the control of the radio network controller 80, the information related to other radio network controllers located in the vicinities of the radio network controller 70, the information related to the base stations that are under the control of the other radio network controllers and the like.
The radio network controller 70 carries out the mobile control with respect to the move of the mobile equipment 90 between the base station apparatuses 80 that are under the control of the radio network controller 70. In addition, with respect to the move of the mobile equipment 90 between the base station apparatus 80 that is under the control of the radio network controller 70 and the base station apparatus that is under the control of another radio network controller, the radio network controller 70 carries out the mobile control by sharing the information of the mobile equipment 90 with the other radio network controller using an interface Iur.
Next, a description will be given of the mobile control in the IMT-2000 system. It is assumed for the sake of convenience that the system structure of the IMT-2000 system is the same as that shown in FIG. 2. For example, the radio network controller 701 holds its own identifier “a”, and the radio network controller 702 holds its own identifier “b”.
A description will be given of a case where the mobile equipment 90 moves between areas covered by the base station apparatuses that are under the control of a single radio network controller, by referring to FIG. 3. FIG. 3 is a diagram for explaining a mobile control in the third generation mobile communication system.
In a step S2, the mobile equipment 90 moves from the area covered by the base station apparatus 801 with which the mobile equipment 90 is communicating to the area covered by another base station apparatus 800, for example.
Then, in a step S4, the mobile equipment 90 sends a reconnect request message with respect to the radio network controller 701 via the base station apparatus 800. This reconnect request message includes the identifier “a” of the radio network controller 701 that controls the base station apparatus 801 covering the area in which the mobile equipment 90 was located before moving, and the identifier of the mobile equipment 90. The mobile control is started when this reconnect request message is sent from the mobile equipment 90 to the radio network controller 701.
In a step S6, the radio network controller 701 which receives the reconnect request message from the mobile equipment 90 uses the identifier included in the reconnect request message to judge the radio network controller with which the mobile equipment 90 was communicating before moving, and confirms whether or not the identifier included in the reconnect request message matches the identifier of the radio network controller 701.
Since the identifier included in the reconnect request message matches the identifier of the radio network controller 701 in this particular case, the radio network controller 701 judges that the moving destination of the mobile equipment 90 is within the area covered by the base station apparatus that is under control of the radio network controller 701. Because all of the information related to the mobile equipment 90 is stored within the radio network controller 701 itself, the radio network controller 701 uses the mobile equipment information stored therein to carry out a procedure of resuming the communication with the mobile equipment 90.
Next, a description will be given of a case where the mobile equipment 90 moves between the area covered by the base station apparatus that is under the control of the radio network controller with which the mobile equipment 90 is communicating and the area covered by the base station apparatus that is under the control of another radio network controller, by referring to FIG. 4. FIG. 4 is a diagram for explaining the mobile control in the third generation mobile communication system.
In a step S2, the mobile equipment 90 moves from the area covered by the base station apparatus 801 with which the mobile equipment 90 is communicating to the area covered by another base station apparatus 802, for example.
Then, in a step S4, the mobile equipment 90 sends a reconnect request message with respect to the radio network controller 702 which controls the base station apparatus 802 via the base station apparatus 802. This reconnect request message includes the identifier “a” of the radio network controller 701 that controls the base station apparatus 801 covering the area in which the mobile equipment 90 was located before moving, and the identifier of the mobile equipment 90. The mobile control is started when this reconnect request message is sent from the mobile equipment 90 to the radio network controller 702.
In a step S6, the radio network controller 702 which receives the reconnect request message from the mobile equipment 90 uses the identifier included in the reconnect request message to judge the radio network controller with which the mobile equipment 90 was communicating before moving, and confirms whether or not the identifier included in the reconnect request message matches the identifier of the radio network controller 702.
In a step S8, since the identifier included in the reconnect request message does not match the identifier of the radio network controller 702 in this particular case, the radio network controller 702 judges that the moving destination of the mobile equipment 90 is within the area covered by the base station apparatus that is under control of another radio network controller. Because the radio network controller 702 does not store all of the information related to the mobile equipment 90, the radio network controller 702 carries out a procedure of acquiring the information related to the mobile equipment 90 from the radio network controller holding the identifier included in the reconnect request message.
In a step S10, the radio network controller 702 which acquires the information related to the mobile equipment 90 carries out a procedure of resuming the communication with respect to the mobile equipment 90.
However, the following problems are encountered in the systems described above.
Generally, in the third generation mobile communication system having the radio network controllers, several tens to several hundred base stations are provided with respect to one radio network controller. For this reason, the geometrical range covered by the base stations that are under the control of a single radio network controller is several tens to several hundred times the area covered by one base station. Consequently, the mobile control for the case where the mobile equipment moves between areas covered by the base station apparatuses that are under the control of a single radio network controller is more dominant compared to the mobile control for the case where the mobile equipment moves between the area covered by the base station apparatus that is under the control of the radio network controller with which the mobile equipment is communicating and the area covered by the base station apparatus that is under the control of another radio network controller.
In addition, in the third generation mobile communication system, the number of radio network controllers provided in the vicinity of one radio network controller is not large. Hence, the information of the adjacent radio network controllers may be stored, as system data, within each radio network controller, so as to identify with relative ease the radio network controller at the moving destination of the mobile equipment.
For example, the information between two radio network controllers is exchanged via the interface Iur which provides an interface between the two radio network controllers. The radio network controller 70 that is started sets a connection to the radio network controllers provided in the vicinity of the radio network controller 70. Moreover, each radio network controller stores, as the system data, the information of the radio network controllers that have a possibility of making a communication therewith. As shown in FIG. 5, for example, if the radio network controller 702 receives the identifier of the radio network controller 703, as the information of the radio network controller that manages the base station apparatus covering the area in which the mobile equipment 90 was located before moving, the radio network controller 702 is able to know the location of the radio network controller 703 by referring to the system data stored in the radio network controller 702, thereby making it possible to recognize the radio network controller 703 to which the information of the mobile equipment 90 is to be inquired. FIG. 5 is a diagram for explaining the transmission and reception of the mobile equipment information in the third generation mobile communication system.
On the other hand, in the future radio communication systems, it would be desirable to implement a portion of the functions provided in the radio network controllers into the base station apparatuses, so as to simplify the network structure. For this reason, the LTE system implements a portion of the functions provided in the radio network controllers into the base station apparatuses. In other words, the management of the mobile equipment is made for each area that is relatively small. As a result, it may be seen that the following inconveniences (1) and (2) will occur, and that there is a need to simplify as much as possible the mobile control for the case where the mobile equipment moves between management areas that are covered by different base station apparatuses.
(1) The proportion of the mobile control for the case where the mobile equipment moves between management areas that are covered by different base station apparatuses increases; and
(2) The number of other management areas located in the vicinity of the management area in which the mobile equipment is located increases.
Under such conditions, it is difficult to store in each base station apparatus the information of the adjacent base station apparatuses as a means of identifying the other management areas of the adjacent base station apparatuses. Consequently, there is a demand to realize the mobile control between the adjacent base station apparatuses that does not require the information of the adjacent base station apparatuses to be stored in advance, that is, does not require the network structure to be recognized.